SB200 Problem/help needed

[ZL3DMH]

50ma might indicate that only one tube is drawing current.

In standby the grid voltage on each tube should be right around -125V. With the amp keyed but NO RF it should be around -2.5V.

There is nothing wrong with a 5W resistor as long as its not masking a problem.

Carl

Hi Carl thank you for your reply, I will fit this 5W resistor then to see if I eliminate this high reading on the plate at idle and among other tests I yet have to do I will check this voltage reading too if I Succeed..

Regards
Doug

[W1QJ]

Although checking every single part on a board can't hurt it is sort of a novice approach. When one understands the workings of the board or the unit as a whole such as this SB-200, going to the source of the problem rather quickly is easy. If the OP has the correct HV reading on the meter that leaves only about 2 resistors left on the board that could be suspect. Then, if the correct idle current is read on the meter when in transmit no drive, the remaining parts on the PS board are good and there is no need to look there for a problem. If the 1 ohm resistor on the PS board is good and is in fact 1 ohm, and he reads 50ma of idle current, this could mean only one tube is drawing current. I would immediately be suspect of a bad tube right away. My next move would be to find out for sure. I would always check the 33 ohm resistors on the tube sockets and make sure they are very close to 33 ohms and that both resistors are close to each other in value. Many times these resistors are way out of spec or even bad. Next it is important to check the grid grounding caps. There are only about 6 problem areas with an SB-200 that cause 90% of the problems. Usually one of them can be identified in a matter of minutes. Naturally it helps to have a coule of pertinent pieces of test equipment all of which cost less than any simple repair by a technician.